The present invention relates to automatic contrast control of a liquid crystal display device for use in a personal computer etc.
Conventionally, contrast adjustment of the liquid crystal display is effected manually by increasing on decreasing a drive voltage applied to a liquid crystal. For example, in contrast adjustment of a liquid crystal display device used in a personal computer, on adjusting volume resistor or variable resister is manipulated by an operator to obtain an optimum contrast of the display in a well known manner.
However, in the conventional manual adjustment method, the adjusting volume resistor must be exposed on an outerior of the display device, thereby causing difficulty, particularly, mechanical and exterior design of a portable display device such as a handy display terminal. Further, some type of the display device is not provided with the adjusting function, and, instead, it uses highly precise components so as to improve accuracy of drive voltage applied to the liquid crystal, thereby causing increase in production cost and degradation in reliability.